BT Sport - shift from getting it via BT Subscription

I only just noticed that plusnet is offering BT Sport. I guess maybe some announcement went in my spam box months ago...Anyhow, I'm paying BT directly for BT Sport right now. It would be cheaper to buy it via plusnet, it seems. What's the best way to make the switch, without losing service, or paying twice? I guess I have to cancel the one (giving notice) and start the other. Has anyone done this? Got any tips?Cheers